This diploma thesis deals with the investigation of the metal-assisted catalytic etching (MaCE) of Si. One of the main goals is to study fabrication of stamps for nanoimprint lithography using MaCE. Formation of nanoporous silicon (PSi), Si nanowires (SiNWs) and three-dimensional nanostructures in Si by MaCE is demonstrated. For this purpose optical lithography, electron beam lithography (EBL), shadow mask evaporation and aerosol nanoparticles deposition techniques have been utilized. The etching rate and surface morphology of Si (with Au lift-off films as a catalyst) as functions of time and concentrations of chemicals are measured in the current diploma work using optical microscope and scanning electron microscopy (SEM). In the current thesis it is shown that Si structures with sub-150 nm lateral sizes, high aspect ratio (up to 1:21), well-defined shapes, and various complexity can easily be fabricated by means of MaCE process.

Current research in materials science and engineering continues to drive it's attention to systems on the nanoscale. Thin films, nano-particles, quantum dots, nano-wires, etc are just a few of the areas that are becoming important in projects ranging from biomedical transport to nano-gears. Thus, understanding, producing, and creating these system is also becoming an important challenge for scientists and engineers to overcome. Physically manipulating objects on the atomic scale requires more than just "micro tweezers" to arrange them in a particular system. Another concern is that forces and interactions that could be ignored or approximated at larger scales no longer hold in this regime. It is the goal of this project to use computational models to simulate nano-particles interacting with customized, highly tailored surfaces in order to confine and pattern them to desired specifications. The interactions to be considered include electrostatic attraction and repulsion, hamaker forces, steric effects, dielectric effects of the medium, statistical variability, mechanical induced surface vibrations, etc. The goal is to be able to manufacture such systems for experimentation in order to compare results to the models. If the models do not hold, we hope to understand the origin of these discrepancies in order to create more robust models for this length scale. Lithography, CVD, and chemical etching will be the primary methods used to create these surfaces on glass substrates. TEM analysis will be compared to modeling through various MD program packages. / Singapore-MIT Alliance (SMA)

Submitted by Charles Jourdan Alberti (charles.alberti@gmail.com) on 2018-08-23T18:57:45Z No. of bitstreams: 1 dissertacao-charles-corrigida.pdf: 2978175 bytes, checksum: bee02fe73d0c98fc3a8035c5f68d9e02 (MD5) / Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2018-09-03T14:51:27Z (GMT) No. of bitstreams: 1 alberti_cj_me_sjc.pdf: 2978175 bytes, checksum: bee02fe73d0c98fc3a8035c5f68d9e02 (MD5) / Made available in DSpace on 2018-09-03T14:51:27Z (GMT). No. of bitstreams: 1 alberti_cj_me_sjc.pdf: 2978175 bytes, checksum: bee02fe73d0c98fc3a8035c5f68d9e02 (MD5) Previous issue date: 2018-07-03 / A modificação da superfície dos implantes é alvo de inúmeros estudos com o intuito de desenvolver alterações microestruturais no titânio e suas ligas que possam acelerar o processo de osseointegração. O futuro da implantodontia está atualmente vinculado a estas futuras descobertas. O titânio e suas ligas são amplamente utilizadas em aplicações biomédicas devido às suas propriedades de biocompatibilidade e mecânicas. Assim, o objetivo deste trabalho é avaliar o efeito nas propriedades físico-químicas de superfície da liga de Ti6Al4V após o ataque com solução piranha nas temperaturas de 25 °C, 40 °C e 60 °C num tempo constante de 30 min. Para caracterização da superfície foram utilizadas as técnicas de microscopia eletrônica de varredura com espectroscopia de energia dispersiva de raios X, perfilometria óptica, difração de raios X e molhabilidade. Além disso foram realizados ensaios de corrosão por polarização potenciodinâmica e espectroscopia de impedância eletroquímica. Os resultados demonstraram que é possível alterar a textura, a rugosidade da superfície e a resistência à corrosão da liga com a variação da temperatura de ataque químico. O tratamento de superfície proposto não alterou a molhabilidade, que se manteve hidrofílica, nem a química da superfície, que se manteve formada principalmente por TiO2 amorfo. A rugosidade e a área da superfície aumentaram exponencialmente com o aumento da temperatura, que pode estar relacionado com o aumento da cinética de reação. Pôde-se obter uma textura tridimensional do tipo esponja com formação de nano e micropits, de acordo com a temperatura de tratamento. Houve um aumento da resistência à corrosão com o aumento da temperatura de tratamento, que pode estar associado com o aumento da espessura do óxido formado. Considerando que tais propriedades são resultados indiretos de potencial sucesso na osseointegração de um implante dentário, o tratamento de superfície da liga de Ti6Al4V com o uso de solução piranha com o controle da temperatura de ataque é um método atrativo e com grande potencial para ser comercialmente aplicado pela indústria de produção de implantes dentários. / The surface’s modification of the implants is the subject of numerous studies with the intention of developing microstructural changes in titanium and its alloys that can accelerate the osseointegration process. The future of implantology is currently linked to these future discoveries. Titanium and its alloys are widely used in biomedical applications because of their biocompatibility and mechanical properties. Thus, the objective of this work is to evaluate the effect on the surface physicochemical properties of the Ti6Al4V alloy after the piranha solution attack at temperatures of 25 °C, 40 °C and 60 °C at a constant time of 30 min. To characterize the surface were used the techniques of scanning electron microscopy with dispersive energy X-ray spectroscopy, optical profilometry, X-ray diffraction and wettability. In addition, corrosion tests were carried out by potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that it is possible to change the texture, surface roughness and corrosion resistance of the alloy with the variation of the etching temperature. The proposed surface treatment did not alter the wettability, which remained hydrophilic, nor the surface chemistry, which remained mainly amorphous TiO2. Roughness and surface area increased exponentially with increasing temperature, which may be related to the increase in reaction kinetics. It was possible to obtain a sponge-like threedimensional texture with formation of nano and micropits, according to the treatment temperature. There was an increase in corrosion resistance with increasing treatment temperature, which may be associated with the increased thickness of the oxide formed. Considering that such properties are indirect results of potential success in the osseointegration of a dental implant, the surface treatment of the Ti6Al4V alloy with the use of piranha solution with the control of the attack temperature is an attractive method and with great potential to be commercially applied by the dental implant production industry.

Visible light emitting diodes (LEDs) are widely used in daily consumer electronics systems, such as general lighting, displays, communication, sensing, and also biomedical applications. To mitigate the ever increasing technology demand, there are tremendous on-going efforts in improving material properties and micro-fabrication techniques. In general, visible LEDs are environmentally friendly, robust and reliable light emitters with small device footprint, and are capable of delivering high luminous efficacy. Typically, LEDs rely on group-III-nitride materials to generate visible light. One of the techniques to generate white light is to coat blue LEDs with yellow phosphor, or ultraviolet (UV) LEDs with red-green-blue (RGB) phosphor. Other scheme relies on combination of RGB LEDs, where high brightness green and blue LEDs are generally grown on robust sapphire substrate. But the current challenges in high threading dislocation density of III-Nitride materials on sapphire or hetero-substrate, phosphor degradation, and bulk-LED mechanical design constraints imposed by the supporting substrate wafer motivate further scientific investigations into strain-engineering, novel reliable phosphor-semiconductor, color-tuning techniques, and transferrable III-nitride vertical LEDs. The current research presents a significant step towards the utilization of annealed porous GaN as a template for subsequent growth of fully relaxed GaN-based epitaxy materials. In our study, we observed significant compressive strain relaxation of 0.41 ± 0.04 GPa in annealed porous GaN fabricated using UV-assisted electroless etching. Moreover the use of GaN nanoparticles with large wavelength tunability and 10 µm InGaN microstructures with different indium composition ushers a new way of making reliable phosphor for white light generation. We also investigate the epitaxial lift-off of InGaN LED structures by selectively etching unintentionally doped GaN sacrificial buffer layer. High GaN/InGaN etching selectivity of 100/1 and with GaN lateral etch-rate of 5 µm/min was achieved using the photo assisted electroless etching process. The kinetics of electron hole transfer in the diffusion limited etching reaction is discussed. Transferred LEDs onto flexible and glass substrates showed ~10 times higher optical power output, 2 times lower series resistance and a lower turn-on voltage than bulk LEDs fabricated from the same wafer. This innovative technique offers a low cost optoelectronic platform for the formation of pixelated red, green and blue (RGB) display on any flexible, transparent or rigid substrates. The technique will also enable new platform for sensing, wearable electronics/optoelectronics and biomedical applications.

Chalcogenide glasses and glass-ceramics present a high interest for the production of thermal imaging lenses transparent in the 3-5 μm and 8-12 μm windows. However, chalcogenide glasses are conventionally synthesized in sealed silica ampoules which have two major drawbacks. First, the low thermal conductivity of silica limits the sample dimensions and second the silica tubes employed are single use and expensive, and represent up to 30% of the final cost of the material. The present work therefore addresses the development of innovative synthesis methods for chalcogenide glass and glass-ceramics that can present an alternative to the silica tube route. The method investigated involves melting the raw starting elements in reusable silica containers. This method is suitable for the synthesis of stable chalcogenide glasses compositions such as GeSe₄ but uncontrolled crystallization and homogenization problems are experienced for less stable compositions. The second approach involves preparation of amorphous chalcogenide powders by ball milling of raw elements. This mechanosynthesis step is followed by consolidation of the resulting powders to produce bulk glasses. Hot Uniaxial Pressing is suitable for compositions stable against crystallization. However, uncontrolled crystallization occurs for the unstable 80GeSe₂-20Ga₂Se₃ glass composition. In contrast consolidation through Spark Plasma Sintering (SPS) allows production of bulk glasses in a short duration at relatively low temperatures and is appropriate for the synthesis of unstable glasses. A sintering stage of only 2 min at 390°C is shown to be sufficient to obtain infrared transparent 80GeSe₂-20Ga₂Se₃ bulk glasses. This method enables the production of lenses with a 4-fold increase in diameter in comparison to those obtained by melt/quenching technique. Moreover, increasing the SPS treatment duration yielded infrared transparent glass-ceramics with enhanced mechanical properties. This innovative synthesis method combining mechanosynthesis and SPS has been patented in the framework if this study. The controlled etching of 80GeSe₂-20Ga₂Se₃ glass-ceramics in acid solution yields nanoporous materials with enhanced surface area. The porous layer created on the surface of the glass-ceramic is shown to play the role of anti-reflection coating and increase the optical transmission in the infrared range by up to 10%. These materials may have potential for the production of sensors with increased sensitivity in the infrared. The influence of indium and lead addition on the thermal and optical properties of the 80GeSe₂-20Ga₂Se₃ glass has also been assessed. Increased In or Pb contents tend to decrease the Tg of the glasses and shift the optical band gap toward higher wavelengths. A systematic ceramization study emphasizes the difficulty of controlling the crystallization for glasses in the systems GeSe₂-Ga₂Se₃-In₂Se₃ and GeSe₂-Ga₂Se₃-PbSe. No crystallization of the In₂Se₃ and PbSe crystalline phase was obtained. Finally, the possibility of producing rare-earth doped 80GeSe₂-20Ga₂Se₃ glass-ceramics transparent in the infrared region up to 16 μm is demonstrated. Enhanced photoluminescence intensity and reduced radiative lifetimes are observed with increased crystallinity in these materials.

Nanoestructuras de alumina anódica porosa (AAP) têm sido tradicionalmente fabricadas por duas etapas de anodização a temperaturas relativamente baixas (de 0 até 5°C), e usadas como máscaras ideais para formação de vários materiais nanoestruturados. Neste sentido, o objetivo do trabalho foi estudar sistematicamente a formação e a fabricação de nanoestruturas de AAP autoorganizadas por uma só etapa de anodização e posterior aplicação na síntese de nanopartículas e nanofios metálicos. As nanoestruturas auto-organizadas de AAP foram obtidas por apenas uma etapa de anodização em ácido oxálico (H2C2O4) a temperatura ambiente; diferentemente dos processos convencionais onde são utilizados duas ou mais etapas de anodização. As características estruturais dos filmes de AAP foram moduladas através do controle dos parâmetros da concentração da solução, temperatura e potencial de polarização. O procedimento principal, para a obtenção de AAP auto-organizadas apenas por uma etapa de anodização, foi o pós-processamento de abertura dos poros através de um processo de corrosão química. Os resultados obtidos neste trabalho mostraram que o diâmetro médio dos poros apresentou uma dependência linear com a temperatura, potencial e tempo de corrosão química e foi constante em relação à concentração da solução eletrolítica. No entanto, a análise estrutural via microscopia eletrônica de varredura (MEV), mostrou que a circularidade e a ordem dos nanoporos sobre a superfície anodizada melhoraram com o aumento da concentração do eletrólito. A estrutura de AAP com um arranjo hexagonal de poros regularmente distribuídos foi obtida quando a anodização foi realizada em 0,3M de H2C2O4, a 45V e 20°C de temperatura seguido de uma corrosão química a temperatura de 17°C por 102 minutos. Adicionalmente foram obtidos nanopartículas e nanofios metálicos utilizando-se as nanoestruturas de AAP como moldes. Como os filmes de AAP são isolantes a obtenção das nanopartículas e nanofios foi realizado através de um processo de eletrodeposição de corrente alternada (CA). Os resultados deste trabalho mostraram que nanoestruturas de AAP autoorganizadas podem ser fabricadas por uma etapa de anodização controlando o tempo de corrosão química. Os resultados apresentados neste trabalho mostram-se vantajosos em relação aos reportados na literatura, já que normalmente as nanoestruturas de AAP são obtidas mediante processos de anodização em duas etapas e tempos longos de anodização. / Nanostructures of porous anodic alumina (PAA) have been traditionally manufactured by two steps anodization at relatively low temperatures (0 to 5°C) and used as templates suitable for the formation of various nanostructured materials. In this sense, the goal of this work was the fabrication of self-organized porous Anodic alumina nanostructures (AAP) by a one anodization step and subsequent application in the synthesis of metal nanowires and nanoparticles. The self-organized nanostructures of PAA were obtained by just one anodization step in oxalic acid (H2C2O4) at ambient temperature unlike to conventional processes where they are used two or more anodization steps. The structural characteristics of PAA films were modulated through control of the solution concentration, temperature and potential of polarization. The key procedure to obtain the periodic organized PAA by only one step anodization was the post-processing of pore opening through a process of corrosion chemistry. The results of this work showed that the average diameter of pores presented a linear dependence with temperature, time of chemical corrosion, polarization potential and it was constant relative to the concentration of the electrolyte solution. However, the structural analysis via scanning electron microscopy (SEM) showed that the roundness and the order of nanoporos over the anodized surface improved with the electrolyte concentration increasing. The PAA structure with a hexagonal arrangement of pores was obtained when the anodization was held in 0.3 M of H2C2O4, 45V, and 20°C of temperature followed by a chemical corrosion at 17°C of temperature for 102 minutes. Additionally it was obtained nano particles and nano metal wires using the PAA structures as molds. Since the PAA films are insulating, the nanoparticles and nanowire were obtained through an electrodeposition process using alternating current. The results of this work have shown that self-organized PAA nanostructures can be fabricated by one anodization step controlling the time of chemical etching process. The results presented in this work are advantageous in relation to reported in the literature, since normally the structures of PAA are obtained by two step anodization and for long anodization time.

The three-dimensional (3-D) writing capability of a high repetition rate (1 MHz) fiber-amplified femtosecond laser with a wavelength of 522 nm was harnessed together with wet-chemical etching for laser-patterning of 3-D optofluidic microsystems in fused silica glass, by the method of Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). Selective chemical etching of laser irradiated glass with dilute hydrofluoric acid (HF) enabled micro-fabrication of high aspect-ratio embedded micro-channels and fine-period 3-D glass meshes in a 3-D inverted woodpile (IWP) arrangement that permitted high density lab-on-a-chip (LOC) integration of flow channels, reservoirs, glass chromatography columns, and optical circuit devices. Optical waveguides, reservoirs, micro-channels, and IWP structures were first laser patterned and followed by selective wet etching controlled by the polarization orientation of the writing laser. With the laser polarization perpendicular to the scanning direction, the volume nanogratings were aligned perpendicular to glass surfaces to facilitate HF etching and thus created designer shaped micro-channels with the smoothest sidewall surfaces measured at present and terminated with open reservoirs. An array of vertical access holes spaced periodically apart facilitated etching of continuous and highly uniform buried channels of unrestricted length in the glass to interconnect flow channels and reservoirs. Alternatively, laser polarization parallel to the scan direction provided low-loss optical waveguides with nanograting walls resisting the acid etching, providing a convenient one-step laser scanning process of optofluidic microsystems prior to wet etching. For the first time, dual-channel capillary electrophoresis was demonstrated by simultaneous fluorescent detection of separating dyes in a 3-D microsystem having over- and under-passing crossed channels in fused silica. In addition, an on-chip particle counting device based on capillary force to drive analytes through an embedded micro-channel into a calibrated reservoir for particle counting was designed and demonstrated. Further, a new type of glass mesh structure is presented where a 3-D IWP micro-channel array with diamond-like symmetry was integrated inside a micro-channel for capillary electrophoretic chromatography. The FLICE technique thus enables rapid prototyping of fully integrated 3-D optofluidic systems in bulk fused silica glasses for numerous applications, and these provide the groundwork and open new 3-D design approaches for advanced microsystems in the future.

The three-dimensional (3-D) writing capability of a high repetition rate (1 MHz) fiber-amplified femtosecond laser with a wavelength of 522 nm was harnessed together with wet-chemical etching for laser-patterning of 3-D optofluidic microsystems in fused silica glass, by the method of Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). Selective chemical etching of laser irradiated glass with dilute hydrofluoric acid (HF) enabled micro-fabrication of high aspect-ratio embedded micro-channels and fine-period 3-D glass meshes in a 3-D inverted woodpile (IWP) arrangement that permitted high density lab-on-a-chip (LOC) integration of flow channels, reservoirs, glass chromatography columns, and optical circuit devices. Optical waveguides, reservoirs, micro-channels, and IWP structures were first laser patterned and followed by selective wet etching controlled by the polarization orientation of the writing laser. With the laser polarization perpendicular to the scanning direction, the volume nanogratings were aligned perpendicular to glass surfaces to facilitate HF etching and thus created designer shaped micro-channels with the smoothest sidewall surfaces measured at present and terminated with open reservoirs. An array of vertical access holes spaced periodically apart facilitated etching of continuous and highly uniform buried channels of unrestricted length in the glass to interconnect flow channels and reservoirs. Alternatively, laser polarization parallel to the scan direction provided low-loss optical waveguides with nanograting walls resisting the acid etching, providing a convenient one-step laser scanning process of optofluidic microsystems prior to wet etching. For the first time, dual-channel capillary electrophoresis was demonstrated by simultaneous fluorescent detection of separating dyes in a 3-D microsystem having over- and under-passing crossed channels in fused silica. In addition, an on-chip particle counting device based on capillary force to drive analytes through an embedded micro-channel into a calibrated reservoir for particle counting was designed and demonstrated. Further, a new type of glass mesh structure is presented where a 3-D IWP micro-channel array with diamond-like symmetry was integrated inside a micro-channel for capillary electrophoretic chromatography. The FLICE technique thus enables rapid prototyping of fully integrated 3-D optofluidic systems in bulk fused silica glasses for numerous applications, and these provide the groundwork and open new 3-D design approaches for advanced microsystems in the future.

Nanoestructuras de alumina anódica porosa (AAP) têm sido tradicionalmente fabricadas por duas etapas de anodização a temperaturas relativamente baixas (de 0 até 5°C), e usadas como máscaras ideais para formação de vários materiais nanoestruturados. Neste sentido, o objetivo do trabalho foi estudar sistematicamente a formação e a fabricação de nanoestruturas de AAP autoorganizadas por uma só etapa de anodização e posterior aplicação na síntese de nanopartículas e nanofios metálicos. As nanoestruturas auto-organizadas de AAP foram obtidas por apenas uma etapa de anodização em ácido oxálico (H2C2O4) a temperatura ambiente; diferentemente dos processos convencionais onde são utilizados duas ou mais etapas de anodização. As características estruturais dos filmes de AAP foram moduladas através do controle dos parâmetros da concentração da solução, temperatura e potencial de polarização. O procedimento principal, para a obtenção de AAP auto-organizadas apenas por uma etapa de anodização, foi o pós-processamento de abertura dos poros através de um processo de corrosão química. Os resultados obtidos neste trabalho mostraram que o diâmetro médio dos poros apresentou uma dependência linear com a temperatura, potencial e tempo de corrosão química e foi constante em relação à concentração da solução eletrolítica. No entanto, a análise estrutural via microscopia eletrônica de varredura (MEV), mostrou que a circularidade e a ordem dos nanoporos sobre a superfície anodizada melhoraram com o aumento da concentração do eletrólito. A estrutura de AAP com um arranjo hexagonal de poros regularmente distribuídos foi obtida quando a anodização foi realizada em 0,3M de H2C2O4, a 45V e 20°C de temperatura seguido de uma corrosão química a temperatura de 17°C por 102 minutos. Adicionalmente foram obtidos nanopartículas e nanofios metálicos utilizando-se as nanoestruturas de AAP como moldes. Como os filmes de AAP são isolantes a obtenção das nanopartículas e nanofios foi realizado através de um processo de eletrodeposição de corrente alternada (CA). Os resultados deste trabalho mostraram que nanoestruturas de AAP autoorganizadas podem ser fabricadas por uma etapa de anodização controlando o tempo de corrosão química. Os resultados apresentados neste trabalho mostram-se vantajosos em relação aos reportados na literatura, já que normalmente as nanoestruturas de AAP são obtidas mediante processos de anodização em duas etapas e tempos longos de anodização. / Nanostructures of porous anodic alumina (PAA) have been traditionally manufactured by two steps anodization at relatively low temperatures (0 to 5°C) and used as templates suitable for the formation of various nanostructured materials. In this sense, the goal of this work was the fabrication of self-organized porous Anodic alumina nanostructures (AAP) by a one anodization step and subsequent application in the synthesis of metal nanowires and nanoparticles. The self-organized nanostructures of PAA were obtained by just one anodization step in oxalic acid (H2C2O4) at ambient temperature unlike to conventional processes where they are used two or more anodization steps. The structural characteristics of PAA films were modulated through control of the solution concentration, temperature and potential of polarization. The key procedure to obtain the periodic organized PAA by only one step anodization was the post-processing of pore opening through a process of corrosion chemistry. The results of this work showed that the average diameter of pores presented a linear dependence with temperature, time of chemical corrosion, polarization potential and it was constant relative to the concentration of the electrolyte solution. However, the structural analysis via scanning electron microscopy (SEM) showed that the roundness and the order of nanoporos over the anodized surface improved with the electrolyte concentration increasing. The PAA structure with a hexagonal arrangement of pores was obtained when the anodization was held in 0.3 M of H2C2O4, 45V, and 20°C of temperature followed by a chemical corrosion at 17°C of temperature for 102 minutes. Additionally it was obtained nano particles and nano metal wires using the PAA structures as molds. Since the PAA films are insulating, the nanoparticles and nanowire were obtained through an electrodeposition process using alternating current. The results of this work have shown that self-organized PAA nanostructures can be fabricated by one anodization step controlling the time of chemical etching process. The results presented in this work are advantageous in relation to reported in the literature, since normally the structures of PAA are obtained by two step anodization and for long anodization time.

High-temperature reactors make use of tri-structural coated fuel particles as basic fuel components. These TRISO particles consist of fissionable uranium dioxide fuel kernels, about 0.5 mm in diameter, with each kernel individually encased in four distinct coating layers, starting with a porous carbon buffer, then an inner pyrolytic carbon (IPyC) layer, followed by a layer of ceramic silicon carbide (SiC) and finally an outer pyrolytic carbon layer (OPyC). Collectively, the coating layers provide the primary barrier that prevents release of fission products generated during burn up in the UO2 fuel kernel. It is crucial to understand how the fission products contained within the fuel interact with the coating layers and how they are distributed within the fuel. The first step commonly performed to obtain the information on distribution is removal of the coating layers. The purpose of this study was to investigate the possible use of wet chemical etching techniques with the aim of removing the coating layers of ZrO2 coated fuel particles in a controlled way and to establish experimental parameters for controlled dissolution of irradiated fuel particles. Stepwise dissolution of coated fuel particle coating layers, containing zirconia kernels has been investigated by chemical etching experiments with acidic solutions of different mixtures. The heating methods used include heating by conventional methods, hot plates and a muffle furnace, a reflux-heating system and microwave-assisted digestion. The etching mixtures were prepared from a number of oxidizing acids and other dehydrating agents. The capability of each reagent to etch the layer completely and in a controlled manner was examined. On etching the first layer, the OPyC, the reflux heating method gave the best results in removing the layer, its advantage being that the reaction can be carried out at temperatures of about 130 ºC for a long time without the loss of the acid. The experimental results demonstrated that a mixture composed of equal amounts of concentrated nitric and sulfuric acid mixed with chromium trioxide dissolves the OPyC layer completely. The most favourable experimental conditions for removal of OPyC from a single coated fuel particle were identified and found to depend on the etching solution composition and etching temperature. Light microscopy yielded first-hand information on the surface features of the samples. It allowed fast comparison of etched and untreated sample features. The outer surface of particles prior to chemical etching of the outer pyrolytic carbon layer appeared black in colour with an even surface compared to the etched surfaces which appeared to have an uneven metallic grey, shiny texture. The scanning electron microscope (SEM) examination of the chemically treated outer carbon layer samples gave information on the microstructure and it demonstrated that the outer pyrolytic carbon layer could be readily removed using a solution of HNO3/H2SO4/CrO3, leaving the exposed SiC layer. Complete removal of the layer was confirmed by energy dispersive X-ray spectroscopic (EDS) analysis of the particle surface. For etching the second layer, the silicon carbide layer, microwave-assisted chemical etching was the only heating technique found to be useful. However, experimental results demonstrated that this method has limited ability to digest the sample completely. Also common chemical etchants were found to be ineffective for dissolving this layer. Only fluoride containing substances showed the potential to etch the layer. The results show that a mixture consisting of equal amounts of concentrated hydrofluoric and nitric acid under microwave heating at 200 ºC yielded partial removal of the coating and localized attack of the underlying coating layers. The SEM analyses at different intervals of etching showed: partial removal of the layer, attack of the underlying layers and, in some instances, that attack started at grain boundaries and progressed to the intra-granular features. The SEM results provide evidence that etching of the silicon carbide layer is strongly influenced by its microstructure. From these findings, it is concluded that etching of the silicon carbide under the investigated experimental conditions yields undesirable results and that it does not provide complete removal of the layer. This method has the potential to etch the layer to some extent but has limitations. Copyright / Dissertation (MSc)--University of Pretoria, 2013. / Chemical Engineering / unrestricted